Past Paper Exam Questions Flashcards
Define the term standard enthalpy of formation.
→ the enthalpy change when one mole of a substance is formed from its constituent elements
→ with all products and reactants in normal states under standard conditions
State why ultraviolet light is needed to produce free radicals.
provides energy to break covalent bonds
Why is % yield important?
Why is atom economy important?
→ the higher the % yield, the higher the efficiency of converting reactants into products
→ a higher atom economy means less waste products and more useful product
Explain why pentan-2-ol has a higher boiling point than pent-1-ene.
→ pentanol has hydrogen bonding
→ pentene only has weak VDW
→ hydrogen bonds are much stronger therefore require more energy to overcome
Define stereoisomers.
molecules with same molecular formula but different arrangement of atoms in space
What is a plasticiser?
a substance that is added to a material to make it softer and more flexible
What is the effect of changing pressure on Kc?
no effect
State the conditions for thermal cracking.
→ high temperature (around 500)
→ high pressure
State the conditions for catalytic cracking. Name its products and uses.
→ slight pressure, high temperature, zeolite catalyst
→ produces branched & cyclic alkanes + aromatic hydrocarbons
→ (motor fuels)
equation for fermentation of glucose
glucose → ethanol + carbon dioxide
Write two propagation step equations to show the decomposition of ozone.
Cl ● + O₃ → ClO● + O₂
ClO● + O₃ → Cl● + 2O₂
Describe how to make a volumetric solution.
- Weigh the sample bottle containing the solid on a (2 dp) balance.
- Transfer solid to beaker and reweigh sample bottle.
- Record the difference in mass.
- Add distilled water and stir with a glass rod until all the solid has dissolved.
- Transfer to a volumetric flask with washings.
- Make up to the 250cm3
mark with distilled water. - Shake flask.
Explain which molecule, ethanal or ethanol, has a higher boiling point and why.
→ ethanol - contains hydrogen bond (bc OH bond is polar)
→ ethanal - only contains VDW (there is no OH bond therefore no hydrogen bond)
→ hydrogen bond is stronger
What does the are under the curve of the Maxwell distribution curve show?
total number of particles
Give an equation for a reaction that removes nitrogen monoxide in a catalytic converter.
2NO + 2CO → N₂ + 2CO₂
What is meant by the most probable energy on a MB curve?
the amount of energy that most particles have (the mode)
State the reagents required to convert aldehyde into alcoholic nitrile.
- KCN
- dilute acid
Explain how anti-bumping granules prevent bumping during reflux.
allows smaller bubbles to form
State the reagent and condition for the formation of an amine from a halogenoalkane in two steps.
→ aqueous alcoholic KCN
→ H2 + nickel catalyst
State why two liquids in an aqueous solution can be separated using a separating funnel.
Liquids are immiscible (don’t mix together)
Explain why polymers do not biodegrade.
carbon-carbon bonds are non-polar therefore are not attacked by nucleophiles
Give one reason why ethanoyl chloride is not used in the industrial synthesis
Corrosive OR forms strong acid/HCl
Explain how carbon dioxide causes global warming.
→ C=O Bonds in CO2 absorb infrared radiation (of 2350cm-1)
→ IR radiation emitted by earth does not escape from
atmosphere
State the meaning of the term complementary when it is used to refer to DNA strands.
(Complementary means the two strands must have base sequences)
that match (all) A to T and C to G
Explain the bonding between two bases.
→ nitrogen & oxygen are very electronegative so C=O & N–H are polar
→ results in formation of a hydrogen bond between O and H
→ in which a lone pair of electrons on an oxygen atom is strongly attracted to δ+H
Explain why simple alkanes/alkenes are not biodegradable.
→ no polar bonds
→ cannot be attacked by nucleophiles
Explain why these practical steps are followed in a purification by recrystallisation experiment:
→ cooling flask to room temp before crystallisation
→ compressing crystals in the funnel
→ cold water poured through crystals
→ lower yield if warm
→ to ensure air passes through the sample, not around it
→ to wash away soluble impurities
State why a minimum quantity of hot water is used in a recrystallisation experiment.
ensures solution is saturated to allow crystals to form
Name three uses of phenylamines.
- making dyes
- making quaternary ammonium salts
- making (cationic) surfactants
Give three reasons why TMS is used as a standard in 13C n.m.r. spectroscopy.
- inert
- low boiling point
- produces one single peak
Reagent for the reduction of benzene into cyclohexane.
H2 (Ni / Pt)
Bond angle in benzene and in cyclohexane.
→ benzene 120
→ cyclohexane 109.5
Equation for concentrated sulfuric acid and concentrated nitric acid.
HNO₃ + 2H₂SO₄ → NO₂⁺ + 2HSO₄⁻ + H₃O⁺
use for quaternary ammonium salts?
cationic surfactants
